1. Field of the Invention
The present invention relates to a telephony communication device, and, in particular, to a line interface circuit for interfacing telephone systems. The line interface enables both voice and non-voice operations at a telephone terminal with a common design. The present invention further relates to a method for controlling the line interfacing circuit.
2. Description of the Related Art
Circuits have been developed to interface communications devices with a telephone exchange system, such as a transmitter/receiver circuit in a standard telephone. Some communications devices, such as a conventional facsimile machine, are designed for both voice and non-voice communications. In one mode, the facsimile machine transmits and receives images of documents or still pictures via a telephone line. Hence, the facsimile machine includes an interfacing circuit having an image processing unit for scanning and digitizing the documents and pictures for transmission via the telephone line. In a second mode, the facsimile machine can be used for voice communications for enabling a user to orally communicate with the intended recipient of the facsimile. Hence, the facsimile machine also includes a voice processing unit, generally within the interfacing circuit, for digitizing sound.
With reference to FIG. 1 there is shown a block diagram of a conventional facsimile machine. The facsimile machine includes a central processing unit or CPUFAX 101 which controls the operations of the facsimile machine, such as transmitting, receiving and copying. The CPUFAX 101 may be provided with an associated RAM memory and stored operating program for operating the facsimile machine or CPUFAX 101 may be connected to an external memory 109. The CPU associated RAM may also store other data including data generated during the execution of the operating program.
An operating panel (OPE) 102 which includes a key matrix having a plurality of keys and a display unit is coupled to the CPUFAX 101. The key matrix includes circuitry for generating at least one signal when a user depresses one of the keys to set a desired operational mode and/or to initiate an operation. Circuitry associated with the display unit of the OPE 102 receives the at least one signal from the control unit 101 and displays an appropriate display element such as LCD(s) indicative of the operational mode or operation being executed by the facsimile machine.
The facsimile machine further includes a sensor unit 103, a scanner 104 and an image processing unit 105. The sensor unit 103 senses the placement of a document in the facsimile machine and whether there is printing paper and generates appropriate signals which are transmitted to the CPUFAX 101. The scanner 104 scans the document and converts the scanned image into digital data which are sent to the image processing unit 105. The image processing unit 105 processes the digital data and transmits the data via a telephone line to a receiving facsimile machine or other communication device.
A printing unit 106 is also coupled to the CPUFAX 101 for printing image data during the receiving or copying operations. The facsimile machine further includes a modem 107 (a non-voice terminal) for performing data communications via a telephone line. In a transmitting mode, the modem 107 modulates the digital data received from the image processing unit 105 and transmits the modulated data under the control of the CPUFAX 101. In a receiving mode, the modem 107 demodulates coded image signals received via the telephone line to re-create the original document data.
A line interface unit (LIU) 108 is coupled between the modem 107 and the telephone line. The LIU 108 establishes a channel between the modem 107 and the telephone line to facilitate: interfacing the telephone line with the modem 107; interfacing the telephone line with a telephone handset; processing of a ring signal received from an exchange system; and telephone dialing operations. The LIU 108 has a tip terminal T and a ring terminal R which are coupled to the telephone line. The above-mentioned functions of the LIU 108 will now be described with reference to FIG. 2.
First, the function of interfacing the telephone line with the modem 107 will be described.
In facsimile data communications, a non-voice path (NVP) is selected by switch unit 110 in response to a switch control signal S1 received from the CPUFAX 101 to trip a switch therein to couple the tip terminal T and ring terminal R to the modem 107 via a first dialer 120 and a first LIU 130 to establish a DC loop. The first LIU 130 serves to transmit signals such as modulated facsimile signals and dual tone multi-frequency (DTMF) dial signals generated from the modem 107 to the telephone line. The first dialer 120 generates the dial pulses.
In addition to selecting a non-voice path, the switch unit 110 can select a voice path (VP) along a second LIU 135, a speech network 150 and a handset 180 to perform a telephone hook switching function. This is accomplished by transmitting a control signal S2 from the CPUFAX 101 to the first dialer 120 to cut-off the DC loop and generate dial pulses. The first LIU 130 serves to keep an AC impedance matching with telephone exchange system EXH by carrying out primary/secondary separating functions, an AC signal coupling function, and a DC masking function.
The function of interfacing the telephone line with the telephone handset 180 to perform voice communications will now be described with respect to the CPUFAX 101 being in a power-on state and in a power-off state. When the user lifts the handset 180 the facsimile is thrown into a DTMF dial mode and the CPUFAX 101 is in the power-on state. In the DTMF dial mode, the speech network 150 can perform various functions such as an inter-conversion between speech signals and electrical signals, inter-conversion between two-wire signals and four-wire signals, AC impedance matching, a DC masking, and a speech transmitting and receiving function. The power-on state is sensed by a hook detector (not shown) which sends a hook-off status signal to the CPUFAX 101 to thereby prepare the modem 107 for a dialing operation via depression of keys on key matrix 250. If the user does not lift the handset, the facsimile is in a dial pulse (DP) dial mode and the CPUFAX 101 controls the first dialer 120 to ready itself for a dialing operation.
In the power-off status of the CPUFAX 101, i.e., when the facsimile machine is in a non-operational mode or emergency mode, a separate hook switch (not shown) connected to the switch unit 110 is mechanically tripped upon lifting of the handset 180 to couple the telephone line to the speech network 150. A bridge diode may be utilized to supply regulated electric power to the telephone line despite variations in the polarity of the electric power.
The dialing operation is initiated by switching the second dialer 170 to the DTMF/DP dial mode by lifting the handset 180 as noted above. The second dialer 170 is supplied with electric power from the speech network 150 for converting dial data received from the key matrix 250 in a form corresponding to the DTMF/DP dial mode. The converted data from the second dialer 170 is then sent to the speech network 150 for the dialing operation.
The LIU 108 of FIG. 2 is uneconomical and inefficient in terms of its circuit configuration since it has an overlapping design. The LIU 108 uses two dialers 120 and 170, two line interface units 130 and 135, and overlapping DC masking circuits. In addition, there are problems regarding the various functions of the LIU 108.
First, there is a problem regarding the function of interfacing the telephone line with the modem 107 and the telephone handset 180. Since the modem 107 and the speech network 150 have AC impedance and DC masking circuits, respectively, the modem 107 exhibits AC impedance and the speech network 150 exhibits direct current resistance (DCR). Therefore, switching noise may be generated on the telephone line when switching occurs between the telephone handset 180 and the facsimile machine by switch unit 110 to switch from voice to non-voice communications.
Second, there is a problem regarding the dialing operation. Since one dialer 120 is used for the modem path and another dialer 170 for the telephone path, the dialers 120 and 170 are not appropriately designed to be able to execute both voice and non-voice communications. Therefore, one has to switch between dialers to change from voice to non-voice communications and vice versa.
Third, there is a problem with the LIU 108 in recognizing a confirm tone generated during the execution of dialing operation in the power-on mode for a voice communication if the switch unit is switched to the non-voice path. As a result, the user cannot initiate a dialing operation for a voice communication when switch unit 110 is switched to the non-voice path because one cannot hear dial tones through the handset 180. The switch unit 110, which operates under the control of the CPUFAX 101, connects the telephone line to the telephone handset 180 only for a short period after the generation of a digit is ended, and before the next digit is generated. Accordingly, the speech network 150 does not operate throughout the dialing operation. As a result, an abnormal dialing operation occurs because the handset 180 intermittently outputs a dial tone whenever the switch unit 110 switches back to the speech network 150.
Further, when a dialing operation is carried out for a voice communication using the handset 180 in a power-on state of the CPUFAX 101, the second dialer 170 associated with the telephone handset 180 cannot be used for a non-voice communication.
Fourth, the last number redial feature may not work properly in the LIU 108 of FIG. 2, especially when the facsimile machine is in the emergency mode. The information about the last number dialed in the ON state is stored in the memory of the CPUFAX 101 while the last number dialed in the OFF state is stored in the second dialer 170. In this regard, LNR information stored in the CPUFAX 101 and LNR information stored in the second dialer 170 may differ. Therefore, the user may dial an unintended number when executing the LNR feature.
It is therefore an object of the present invention to provide a line interface circuit which includes a circuit configuration having a dialer, a line interface unit (LSU) and a DC masking circuit adapted to execute a dialing operation without switching between two different dialers and two different line interface units, one for voice communications and one for non-voice communications. The present invention also provides a method for controlling the line interface circuit.
It is another object of the present invention to provide a line interface circuit capable of allowing a user to continuously hear dial confirmation tones generated during a voice dialing operation.
Further, it is an object of the present invention to provide a line interface circuit which includes a single unit for storing LNR information, thereby preventing the dialing of an unintended number.
In one embodiment of the present invention, a line interface circuit for interfacing a voice terminal and a non-voice terminal with a telephone exchange via a telephone line, comprises: a single dialer for facilitating communication between the voice terminal and non-voice terminal with said telephone exchange; a communication port coupled to the non-voice terminal; and line interface control unit for receiving dial information from a key matrix input at the non-voice terminal via the communication port in a power-on state, for deriving power during said power-on state from said telephone exchange, for transferring the dial information to the dialer, for directly receiving dial information from the key matrix in a power-off state of the non-voice terminal, and for transferring the dial information to the dialer.
In a second embodiment of the present invention, a method for controlling a line interface circuit used to interface a telephone exchange system with a non-voice terminal and a voice terminal through a telephone line, including the steps of: sensing a hook-off status of a handset equipped to the voice terminal; transmitting a signal indicative of the sensed hook-off status to a main control unit from a line interface control unit of the line interface circuit; checking whether a response to the hook-off status signal is generated by the main control unit within a predetermined time from the time when the hook-off status signal is transmitted; setting an operational mode if it is determined that the response is generated within the predetermined time and coupling the voice terminal to said telephone line upon setting said operation mode; and checking receipt of dial information via the voice path.